1. Field of the Invention
The present invention relates to membrane switches. More specifically, the invention is directed to a membrane switch keyboard apparatus.
2. Description of the Prior Art
Membrane switch keyboards are well-known in the art as shown in U.S. Pat. Nos. 3,860,771; 3,995,126 and 4,423,294. Membrane keyboard devices include an array of elastic bubble members or keys corresponding to an array of individual switching units. The bubble members are actuated or deformed by the touch of an operator to cause the selected bubble member to be deflected whereby to provide a deflection of an associated flexible electrically conductive member to provide an electrically conductive path or bridge between adjacent first and second electrode members. While such membrane keyboard devices have found great acceptance, particularly in the field of computer keyboards, by virtue of the feel of the keyboard during actuation which approximates that of a conventional switch by providing tactile feedback to the operator, they have also inherently exhibited a lack of security by a failure to provide a means for preventing an operation of certain ones of the bubble members by the operator. Thus, if the keyboard is to be limited in certain applications to particular functions, it would be desirable to provide a means to lock out certain ones of the bubble member keys to prevent an operator from either inadvertently or deliberately actuating incorrect keyboard switches and to simplify a keyboard for a particular application by reducing the number of operator accessible keys.